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Mark McLean, David Thompson, Hong-Ping Zhang, Max Brinsmead and Roger Smith

McLean M, Thompson D, Zhang H-P, Brinsmead M, Smith R. Corticotrophin-releasing hormone and β-endorphin in labour. Eur J Endocrinol 1994;131:167–72. ISSN 0804–4643

The objectives of this study were to determine whether the maternal plasma corticotrophin-releasing hormone (CRH) concentration influences the amount of uterine contractility induced by infused oxytocin during induction of labour, and secondly to assess changes in CRH and β-endorphin in response to stress during labour. Serial plasma CRH and β-endorphin measurements were made in 40 women undergoing induction of labour and correlated with uterine contractility, cervical dilatation, length of labour, analgesic usage and fetal distress. The plasma CRH concentration did not change throughout labour. In subjects receiving infused oxytocin there was a significant positive correlation between plasma CRH and the amount of uterine activity, and a high plasma CRH level was associated with shorter labour. The plasma β-endorphin level rose with progressive cervical dilatation and fell after epidural anaesthesia. The plasma CRH level did not correlate with the plasma β-endorphin level or rise with fetal distress. We conclude that high levels of maternal plasma CRH are associated with an increase in the uterine contractile response to infused oxytocin. The maternal plasma CRH level does not vary in response to maternal or fetal stress, but β-endorphin secretion does rise in response to the stress of labour and is influenced by pain perception.

Mark McLean, Endocrine Unit, John Hunter Hospital, Locked Bag 1, Newcastle Mail Centre, Newcastle, NSW 2310, Australia

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Eng-Cheng Chan, Roger Smith, Terry Lewin, Max W Brinsmead, Hong-Ping Zhang, Jeff Cubis, Kathryn Thornton and Di Hurt

To investigate the dynamic relationships among corticotropin-releasing hormone (CRH), β-endorphin (βEP), cortisol and obstetric events during pregnancy, blood samples were collected from 193 women at 28 weeks, 38 weeks, during labour and on the second postnatal day. Cord blood at delivery was also obtained. We found that: (1) Maternal plasma CRH, βEP and cortisol rose from 28 to 38 weeks. (2) During the third trimester maternal plasma CRH and βEP were correlated (r=0.30, p<0.001). (3) During labour, no correlations were found among maternal plasma CRH, βEP and cortisol. (4) Maternal CRH at labour and the duration of labour were not correlated. (5) Maternal plasma CRH tended to be higher in women who delivered early (more than seven days prior to estimated date of confinement [EDC]) relative to those who were on time (within seven days' EDC) or late (greater than seven days after EDC). (6) CRH in maternal plasma at labour and cord blood were correlated (r = 0.29, p<0.05) as were maternal and fetal βEP (r=0.43, p<0.001). (7) Fetal obstetric difficulty was correlated with fetal βEP (r=0.54, p<0.001). Our findings support the hypothesis that maternal plasma CRH regulates maternal βEP during the third trimester, but other factors are involved during labour and in response to maternal obstetric stress.